The present invention relates to a document information detecting apparatus having a document size detection means and a document density detection means, for use in a copying machine forming images with an electrophotographic system.
Located around a revolving image-carrier in a copying machine of an electrophotographic type are a charging means such as a corona charger, an exposure means for illuminating light images and thereby forming latent images, a charge-neutralizing means wherein an LED is used for illumination for forming an image frame, a developing means for developing the latent images to form toner images, a transfer means for transferring the toner images onto a recording sheet and a cleaning means for removing toners remaining on the image-carrier after transferring of the toner images onto the recording sheet has occured.
With regard to the developing means, when it is a developing unit employing developers of a two-component type, carriers and toners are agitated fully in a developer container to become developers wherein toners are attracted triboelectrically onto carriers. The developer are attracted magnetically to a developing sleeve to form a layer around it and are transported to the developing area which faces the image carrier. Latent images on the image-carrier are developed by developers in the developing area into visible images (toner images) in which toners are attracted electrostatically to the latent image portions.
A technique to detect document density for automatic adjustment of image quality in the course of development has been proposed in Japanese Patent Publication Open to Public Inspection No. 93834/1978 (hereinafter referred to Japanese Patent O.P.I. Publication). In addition to that, a technique for charging a bias voltage on a developing roller depending on the background color of a document and the level of image density on the document to thereby automatically adjust the density of a copy image has been proposed in Japanese Patent O.P.I. Publication No. 45564/1982.
When toners are consumed in the course of development and thereby the toner ratio in the developer is lowered to a level that is equal to or lower than the lower limit of a certain range, satisfactory toner images may not be obtained. The occurence of this situation needs to be detected, and then toners need to be replenished into the developing unit promptly. This technique is disclosed in Japanese Patent Examined Publication Nos. 16199/1968 and 46421/1988. With this technique, an electrostatic latent image of a reference patch image having a preset density is formed at a location on a photoreceptor drum which does not come in contact with a recording sheet. Then, this latent image is developed, and the density of the toner image of the reference patch image thus obtained is examined by a photoelectric sensor. When the density of the toner image of the reference patch is lower than a certain preset value, the concentration of toners in the developing unit is determined to be inadequate, and toners are replenished accordingly into the developing unit from a hopper. When the density of the toner image is satisfactory, on the other hand, toners are not replenished. Thus, the density of images formed on a recording sheet can be kept equal to or higher than a certain level.
Further, Japanese Patent O.P.I. Publication No. 22424/1981 discloses a device wherein the reverse side of a document cover (a platen cover) with which a document on a platen glass is brought in contact is provided with a colored portion which is covered partially or entirely by the document so that the document size can be detected.
Heretofore, a copying machine has been equipped with a document size detecting means (called an APS device hereinafter) an image density detecting means (called on EE device hereinafter) and a toner rate detecting means, and thereby automatic size selection and feeding of recording sheets, copy density adjustment and replenishment of toners into a developer have been carried out. For the control of the above-mentioned functions, a central processing unit (CPU) composed of an LSI integrated circuit has been used.
Recently, there is available a CPU having an analog inputting mode wherein analog signals can be processed inside the CPU. Thus, small-sized and inexpensive control devices are attained.
However, as a CPU generally available is provided with a limited number of input ports for analog signals, such CPU is insufficient for a copying machine having many analog signals to be processed through analog input ports. In case of a copying machine, therefore, the analog signals are processed to be converted into digital signals externally outside of a CPU. Therefore, an IC for processing analog signals needs to be added, requiring an additional space and causing a device to be expensive, which has been a problem.
The first object of the invention is to provide a document information detecting device for a copying machine wherein above-described problems may be solved and a CPU having input ports for analog signals fewer in number than normally required for a copying machine can also be used.
In the device mentioned above, many sensors have been used as various types of detecting means, and circuits for each of such sensors have been needed, causing the device to be complicated in structure and to be expensive.
The second object of the invention is to provide a relatively inexpensive copying apparatus wherein one set of sensors can serve two different functions, less adjustment is needed in assembly work, and the number of necessary parts is reduced.